 class exam3_3_2 {
        public static void main(String args[]) {
                double sum = 0;
                int i = 1;
                do {
                        sum=sum+1.0/fact(i);
                        i++;
                }while(i<=20);
                System.out.println(sum);
        }
        public static int fact(int n) {
                if(n==0)
                        return 1;
                else
                        return n*fact(n-1);
        }
}
